The number of sunspots over time

This graph shows how the number of sunspots on the Sun has changed over time. The black curve shows the yearly mean sunspot number from 1700–1749, and the blue curve shows the monthly sunspot number (smoothed over 13 months) rom 1749 up to the present.

Sunspots are regions where the Sun’s magnetic field is particularly strong. They look like dark spots on the Sun's visible surface (the photosphere) because the strong magnetic field restricts the motion of charged particles, making them cooler than their surroundings.

The number of sunspots shows clear peaks and troughs, corresponding to the solar cycle. The peaks correspond to the solar maximum, which is when the Sun is at its most active. The troughs correspond to the solar minimum, when the Sun is at its most calm.

The graph is provided by the World Data Center for the Sunspot Index and Long-term Solar Observations (WDC-SILSO), part of the Solar Influences Data analysis Centre (SIDC) of the Royal Observatory of Belgium. Apart from determining the internationally recognised sunspot number, SILSO uses historical data and sophisticated models to predict how the solar cycle will progress.